Nozzle structure for jet printers

ABSTRACT

An ink jet nozzle structure comprising a thin tube, connected to a pressurized ink reservoir, is encircled by an A. C. driven coil which induces longitudinal reciprocating motion to cause formation of ink droplets. A permanent magnet is in the proximity of the drive coil provides a biasing action. The tube length is chosen so as to permit it to vibrate resonantly at the frequency of the induced longitudinal reciprocating motion. Resonant vibration permits the tube to be supported at two points along its length greatly increasing its mechanical stability. An air damper located near the tip of the nozzle broadens the resonant response and provides differential signals proportional to the longitudinal movement of the tube to maintain movements at a fixed or preset level.

United States Patent Haskell 1 June 6, 1972 54 NOZZLE STRUCTURE FOR JET3,512,172 5 1970 Colecchi ..346/140 x PRINTERS I Y 3 3,361,352 1/1968Ham's ..239/102 x 2,550,771 5/1951 Cam .Q ..239/l02 UX [72] Inventor:John W. Haskell, Endwell, N.Y. p [73] Assigneez' International BusinessMachines Corpora- 'l' Exami' 1erM Benson f on, Armork NIY. AsszstantExamrnen-Remhold W. Thieme Attorney-Hamlin and knew and Andrew Taras[22] Filed: Mar. 13, 1970 v 1 [211' Appl. No.: 19,367 [57] ABSTRACT 1 Anink jet nozzle structure comprising a thin tube, connected 52 us. Cl..;.....239/102, 346/140 f l l by f- [51] Int. Cl... ..B05b 3/14 g il' Ti rec'pmcatmg 9"? cause orma ion 0 1n rop ets. permanent magnet 18 n t eprox- [58] Field ofSearchWr 39/102,346/75, 141) imity of the drive coilprovides a biasing action. The tube I length is chosen so as to permitit to vibrate resonantly at the [56] Referencesclted frequency of theinduced longitudinal reciprocating motion. V UNITED'HSTATES PATENTSResonant vibration permits the tube to be supported at two 1 pointsalong its length greatly increasing its mechanical stabili- 3,334,3508/1967 Adams ..346/75 An air damper located near he fip f the nozzlebroadens 342141101 10/1965 "239/102 the resonant response and providesdifi'erential signals propor- 3,231,359v 4 2 32 tional to thelongitudinal movement of the tube to maintain 3,400,392 9 l Ensminger;movements at a fixed or reset level. 3,155,141 11/1964 Doyle et al........239/1'02 X" y p f 3,281,860 10/1966 3 Claims, 5 Drawing FiguresAdams et al. ..239/102 X SHIELDED CABLE FEEDBACK CONTROL /IFTEXPERMANENT 1411111511 181E METAL SllIELD RESERVOIR v TUBlNC 4 DRIVE c0115NODE 26 PATENTEDJUH 6 L972 3. 667, 678

I SHIELDED CABLE FEEDBACK CONTROL} FIG. I WEFIWNiL .L

ADHERENT LAYER OF COPPER THIN METAL PLATEH 1c I s 18 ..::z I I Iz'iiijiii 7 v TUBING1 10 L E 1 Q L2r 11 5: E a \LNSULATION L L N kw E LE X B L E L I PERMANENT MAGNET L WINK I LNSULATED E I 4 RESERVOIE sLEEvEH6 3 FIG. 2

DRlV coLLs" 6 E i8 W i FLEXIBLE CONNECTLONTOINK :1; RESERVOIR i j L E NJ 1 PERMANENT MAGNEH/ I H6 4 18b lNVEA/TOR TUBING JOHN w. HASKELL i8AGE/VT FIG. 5

BACKGROUND OF THE INVENTION The'formation of uniformink droplets and thecharging of each individual droplet with a precise charge has not beentoo successful by prior art ink jet printers. Non-uniform or satellitedroplet formation has been a continuing problem due to the presence ofnon-sinusoidal vibration in the jet nozzle. The rior art fails toprovide any satisfactory means for operating closely spaced groups ofink jets where precise positioning of individual jets is required.Although specific nozzle designs have been produced with a modest degreeof success, they have been held to limited speeds of operation beyondwhich reliability suffers and print quality deteriorates.

OBJECTS The principal object of the invention is to overcome the citeddisadvantages in prior art jet printers by providing an improved jetprinter nozzle structure which is highly reliable, faster in operationand more accurate in printing quality than the prior art ink jetprinters.

Another object is to provide a novel arrangement for the nozzleutilizing dimensional relationships that provide a resonant mode ofoperation to eliminate the formation of satellite drops in the jetstream.

A more detailed object is to improve the stability and performance ofthe nozzle structure by substantially eliminating the dead" area ofresponse before tube movement can occur.

Yet another detailed objectis to provide a nozzle structure which can bepositioned with ease.

Theforegoing and other objects, features and advantages of the inventionwill be apparentfrom the following more particular description ofpreferred embodiments of the invention,

as illustrated in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS- DESCRIPTION OF THE INVENTION The nozzlestructure shown in FIG. 1 comprises a nickel tubing "1 secured within awall opening 2a forming part of an ink reservoir 3 containingpressurized ink admitted by way of an entry port 3, the reservoir 3being secured by' way of suitable means, not shown, to a metal base 4.In proximity to and encircling said tubing 1 is an A. ,C. drive coil 5which when energized induces magnetostrictive action that causesvibrations along the longitudinal axis of the tubing. The tubing I isfurther supported by means of a bracket 6 by virtue of which and inconjunction with opening 2a in the wall f the reservoir 3, node points6a and 2a are established in the tubing. At these node points 6a, 2asubstantially little or no vibrational effects are present, whereasmidway between these two points and at the tube orifice la, maximumvibrational effects exist. By suitable supporting means, not shown, apermanent magnet '7 is disposed abovethe drive coil 5. The permanentmagnet provides a static magnetic bias to the tubing resulting in amagnetostrictive bias of the tubing to eliminate a dead" area ofresponseby virtue of which the movement frequency of the tubingis'stabilized relative to the drive frequency.

Although the invention may be designed to accommodate a variety ofdifferentresonant frequencies, the structure of FIG. 1 has been designedto function at a natural resonant frequency of 50 kHz. in thethree-quarter wavelength mode by virtue of the fact that the nickeltubing is supported at points of maximum force with minimum displacementand the nozzle is located at a point of minimum force'with maximumdisplacement. This construction enhances the sinusoidal character of thevibrational movement and tends to suppress responses at other than theresonant frequency. Since the resonant frequency of the arrangement is afunction of the dimensional relationship of the tubing length on eitherside of the node point 6a, the resonant frequency of 50 kHz. results bylocating the bracket 6 in such a position as to bring the point 6a adistance of one unit of length to the right of the nozzle orifice la,and two units of length from the node point 2a, assuming an entiretubing length of three units of length. The one unit of length tubingsection extending to the left of the node point 60 represents a quarterwavelength of the resonant frequency while the section between the nodepoints 6a, 2a represents a one-half wavelength of the resonantfrequency. Alternatively, the tubing can be resonated in thefive-quarter or sevenquarter wavelength mode or any higher odd multipleof quarter wavelengths by logical extension of this principle. Thus inthe five-quarter mode, one unit of length tubing section extending tothe left of the node point 60 again represents a quarter wavelengthwhile four units of length between node points 60 and 2a represent onewavelength of the resonant frequency. The presence of liquid underpressure in the nickel tubing has a damping effect which broadens theresonant response. v

To further broaden the useful movement amplitude to frequencies of about5 kHz. above and below the resonant frequency of- 50 kHz. and to furtherenable the resonant frequency to be accurately monitored, there isprovided a non-resonant electromechanical damper 10 shown located at theleft end of the tubing 1. The damper as best seen in detail in FIG. 2,comprises a rigid, flat, thin metal plate 11 secured, by suitable knowntechniques, to the outer periphery of the tubing, in the manner shown.Spaced on either side of said plate 11 and disposed in parallel relationthereto are insulating members 121 and I2r suitably secured, in themanner shown, to the base 4. Suitable openings 121 and 12r are providedto allow freedom of movement of the tubing during resonant operations.On the inner face of each of the members 121 and l2r is an'adherent thinlayer of copper. By virtue of this arrangement, a differentialcapacitive mechanism is formed to yield differential signalsproportional to the'movement amplitude of the tubing. These signals areutilized to monitor the resonant frequency, and by means of the feedbackcontrol I4 connected by means of shielded cables, as shown, the drivecoil 5 can be controlled to maintain the tubing movement amplitude atany desired level.

To prevent electrostatic and electromagnetic effects from interferingwith the signals from the differential capacitive mechanism, a flexiblemetal shield 15, shown in dotted, is extended between the bracket 6 andthe reservoir 2 to isolate the effects produced by the drive coil 5.

The nozzle structures shown in FIGS. 3 and 4 are designed to permitaccommodation of a multiplicity of jets in close proximity where eachjet may be positioned individually and all jets share a common drivecoil.

The nozzle structure shown in FIG. 3, is designed for relatively lowfrequency operations. In this arrangement, drive coil 5' is located onbase 4' with the biasing permanent magnet 7 located therebetween. Thedrive coil is located in such a manner as to induce magnetostrictiveeffects upon the portion of the tubing 1' located between the left end'of the nozzle Ia and the node point 6a, the latter beingestablished byvirtue of the position assumed by the bracket 6! To aim the tubing 1' toany desirable direction, a second bracket 18 is provided and located onthe base 4 in the manner shown. As seen from an end view in FIG. 5, eachof the brackets is provided with an elongated slot, open at one end toreceive the tubing. One dimension of adjustment is provided by movingthe nickel tubing vertically between brackets 6' and 18'. A seconddimension of adjustment is provided by rotating the nickel tubing in thebrackets in order to compensate for eccentricity. By virtue of this slotarrangement, each bracket is provided with tines 18a and 18b ofsufficient spring tension to maintain the tubing at any desiredposition. To enable positioning of the tubing, a flexible connection isestablished to communicate with the ink reservoir. I

Still referring to FIG. 3, the length of the nickel tubing between thejet nozzle end la and the nearest support, bracket 6', is adjusted toproduce resonance in the quarter wavelength mode at the vibrationfrequency. The remaining portion of the tubing may be any length thatcan be conveniently accommodated by the second support 18. Thisconfiguration is suitable for'all frequencies where the nickel tubing inthe quarter wavelength mode is long enough to accommodate the drivecoil.

The arrangement shown in FIG. 4 is designed for relatively highfrequency operations. In this arrangement the drive magnet 5" isconveniently located between brackets 18' and 6" and corresponds to theposition assumed by the drive coil 5 in the arrangement of FIG. 1. Forbiasing action permanent magnet 7" is located between drive coil 5" andthe base 4".

The entire length of the nickel tubing shown in FIG. 4 is selected so asto effect resonance in the three-quarter wavelength mode, the tubingsupport brackets 6" and 18a being situated at points of minimumdisplacement. Maximum displacement thus occurs in the middle of the halfwavelength section and at the noule end of the quarter wavelengthsection. This configuration is suitable for higher frequencies where theportion of the tubing in the quarter wavelength mode is too short toaccommodate the drive coil.

Although nickel tubing has been specified in view of its desirablecharacteristics, the invention need not be limited to the use of nickeltubing since other metallic tubing having magnetostrictive propertiesmay be utilized to carry out the desirable features of the invention.

Calculations involving operations at a resonant frequency of 90 kc. forthe structure shown in FIG. 4 yield a wavelength of 2.20 inches for thethree-quarter wave mode, an overall tubing length of 1.65 inches, with a0.55 inch length for the tubing section between the nozzle la and thenode 6a.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein.

What is claimed is:

l. A nozzle vibrator providing a jet stream of individual ink dropletsfor an ink jet printer comprising:

a length of metal tubing having a nozzle at one end thereof;

a reservoir of pressurized ink connected to the opposite end of saidtubing whereby the latter is supported for longitudinal vibration;

a stationary drive coil encircling said tubing for producing analternating magnetic field and inducing magnetostrictive effects thereinto cause longitudinal vibration in said tubing in response to theapplication of a driving frequency to said drive coil, the resonantfrequency of said tubing being a function of the dimensionalrelationships of said tubing and of the driving frequency,

a support means for further supporting said tubing at a node point inthe proximity of the nozzle end of said tubing,

non-resonant damping means interconnected to said tubing to broaden theresonant response thereof, and

means comprising a permanent magnet producing a fixed magnetic field toinduce a constant magnetostrictive bias of said tubing.

2. A nozzle vibrator as in claim 1 in which said damping means isfurther modified by the provision of electrical means providingdifferential signals proportional to the movement amplitude of saidtubing.

3. A nozzle vibrator as in claim 2 further including a feedback controlmeans electrically interconnected to said drive coil and responsive tosaid differential signals to monitor and maintain control over the r sonantjre quency of said tubing.

1. A nozzle vibrator providing a jet stream of individual ink dropletsfor an ink jet printer comprising: a length of metal tubing having anozzle at one end thereof; a reservoir of pressurized ink connected tothe opposite end of said tubing whereby the latter is supported forlongitudinal vibration; a stationary drive coil encircling said tubingfor producing an alternating magnetic field and inducingmagnetostrictive effects therein to cause longitudinal vibration in saidtubing in response to the application of a driving frequency to saiddrive coil, the resonant frequency of said tubing being a function ofthe dimensional relationships of said tubing and of the drivingfrequency, a support means for further supporting said tubing at a nodepoint in the proximity of the nozzle end of said tubing, non-resonantdamping means interconnected to said tubing to broaden the resonantresponse thereof, and means comprising a permanent magnet producing afixed magnetic field to induce a constant magnetostrictive bias of saidtubing.
 2. A nozzle vibrator as in claim 1 in which said damping meansis further modified by the provision of electrical means providingdifferential signals proportional to the movement amplitude of saidtubing.
 3. A nozzle vibrator as in claim 2 further including a feedbackcontrol means electrically interconnected to said drive coil andresponsive to said differential signals to monitor and maintain controlover the resonant frequency of said tubing.